The use of various mechanisms for automatically feeding manufacturing machinery and the like has been widely utilized for centuries in the manufacturing and machine tool industries. One type of conveying system popular to move parts and workpieces along manufacturing assembly lines are known as "walking beam" conveyors, wherein the conveyors are equipped with several barrel cams whose rotation is synchronized to cause the "walking" or orbital movement of a beam along a closed path. The resulting path of movement of the beam in such conveyors is determined by the patterns of the particular cams used, and by continuous rotation of such cams. The beam reciprocably move objects being conveyed as it continuouslY oscillates in a predetermined cycle. However, the drives required to synchronize the motions of the barrel cams used to provide the "walking" motion of the beam are generally complex and sophisticated in nature, and require relative close tolerance in the patterns to prevent undue wear and fatigue which could result from improper synchronization of movement.
A walking beam conveyor which attempted to overcome some of the general problems of multiple-cam driven walking beam systems is set forth in U.S. Pat. No. 4,151,907, which issued to M. Doty on May 1, 1979. The Doty reference describes a walking beam conveyor utilizing a single cam for both vertical and horizontal movement achieved through first and second linkage connections. Doty teaches that the motion of the beam traverses a closed path once for every 360.degree. of revolution of the cam, and that the pattern of the cam groove can be selected to allow a limited pause or "dwell" at each corner of the rectangular path, if desired. Doty further sets forth that changing connections within the linkage system can cause the beam to execute slightly longer or shorter strokes in tracing its movement path for particular applications while the Doty conveyor allegedly simplified the required mechanisms to drive a walking beam conveyor system, the system was rigidly limited to the beam stroke pattern determined by the particular cam groove Pattern and the connection of its linkage structures.
A somewhat similar workpiece feed and removal mechanism is set forth in U.S. Pat. No. 4,209,087, which issued to A. Kushigian on Jun. 24, 1980. The Kushigian mechanism included a walking beam carried by a slide mechanism which was mounted on a supporting table. The walking beam was to be raised and lowered in a generally vertical direction by a hydraulic cylinder, while the slide mechanism was reciprocated on a way by a separate hydraulic cylinder. The extent of forward travel of the slide relative to its way was limited by an adjustable stop screw, and a pair of limit switches were used to control the hydraulic cylinder. The walking beam included a plurality of precisely spaced workpiece cradles which corresponded to similar cradles in the non-moving support structure of the conveyor. Kushigian specifically teaches that the forward movement of the walking beam was to be limited to a distance equal to spacing between the centers of immediately adjacent recesses of the workpiece cradles. Consequently, the Kushigian device was designed to merely move a predetermined number of workpieces spaced from one another at a predetermined distance between adjacent workpiece cradles of a machine tool.
Similarly, U.S. Pat. No. 32,804 which issued to A. Mason on Dec. 20, 1988 (reissue date), sets forth a multiple station conveying mechanism for moving a plurality of workpieces along predetermined machining stations. The Mason transfer mechanism incorporates the use of a link system to vertically lift a shuttle supporting a plurality of workpieces received on locator and supPort pins of the shuttle assembly. Mason requires two full revolutions of its crank to move the shuttle in a generally vertical motion to its fully raised position. Once in its fully raised position, the shuttle is indexed forward to advance each of the workpieces one work station. After advancing the workpieces one work station forward, the crank is rotated in the opposite direction to lower the shuttle and disengage the locators from the workpieces, and thereby allow the shuttle to be retracted to its original position for another indexing cycle.
Other mechanisms, such as those described in U.S. Pat. No. 4,781,285, which issued to H. Schlatter et al. on Nov. 1, 1988, and U.S. Pat. No. 4,783,889, which issued to S. Hayashi on Nov. 15, 1988, describe various other transfer mechanisms for moving objects between predetermined work stations. In both of these mechanisms, the forward movement of the conveyor apparatus, when in fully uplifted position, is limited specifically to the distance between work stations, or between V-shaped notches in the fixed support rails.
In today's highly automated manufacturing facilities and machine shops, it is often desirable to have the ability to move objects along a conveying system without regard to maintaining uniform spacing between the objects, and without having to index the objects to correspond with particular work stations or alignment devices on the conveying system itself. This is especially true in situations where a mechanized loading system is utilized, such as a spot loading robot or similar device which loads one workpiece at a time into and/or out of a particular machine tool. Such situations require feeding of one workpiece at a time to a predetermined loading position. Heretofore, mechanisms available in the industry have relied upon walking beam conveyors and similar mechanisms, as described above, which require items to be transferred to be uniformly spaced and supported within various locator restraints on such conveyors to maintain that predetermined spacing. Reciprocable beam systems or walking beam systems were moved in predetermined patterns with little room for modification or error. Such predetermined spacing further complicated loading procedures, which required maintenance of those predetermined spacing patterns. The systems were inflexible and, consequently, limited in application, and most often require custom designing even for general applications.